Birth defects occur frequently in humans but occurrence in most cases is sporadic without obvious genetic or environmental etiology. The mouse mutation Disorganization (Ds) is an extraordinary example of a single gene Mendelian trait that has sporadic patterns of occurrence because of its exceptional genetic and developmental features. Ds is one of the rare examples of a trait that is inherited in a true-dominant and gain-of-function manner. Its developmental attributes are even more striking. Ds causes an extraordinary variety of birth defects involving most body parts, but remarkably no two mice are affected in the same way. The defects are always asymmetrical but often show mirror-image symmetry in the affected structure. The nature of the various birth defects suggests both that the Disorganization gene plays a fundamental role in pattern formation and lineage determination during embryonic development, and the nature of the mutation leads to unpredictable anomalies in the normal patterns of development. During the previous funding period, we discovered a new insertion of an ETnII transposable element at the Ds locus, and a BAC with this element and three flanking genes that can cause Disorganization-like birth defects in transgenic mice. However, the location of this ETnll insertion between genes suggests that it did not disrupt coding sequences, but instead may cause chimeric transcripts, it may adversely affect the expression of flanking genes, or the insertion may have disrupted a non-coding functional element. To identify the Ds gene, we propose Specific Aim 1: to complete the comparison between the finished sequence in Ds mice with the corresponding sequence in the DA/Hu strain on which the Ds mutation arose; Specific Aim 2: to test expression patterns (chimeric transcripts and mRNA levels) of the three candidate genes during embryonic development in DS/Ei and DA/Hu embryos; and Specific Aim 3: to test for affected mice in BAC transgenics, ETnll knock-in mutants at the Ds locus in wild-type mice, and the functional consequences of ubiquitous over-expression of each of the three flanking genes in wild-type mice. These systematic studies should lead to identification of the Disorganization gene and to insights into the control of fundamental developmental processes and the ways in which sporadic birth defects arise. [unreadable] [unreadable] [unreadable]